i would buy them full length which is 32".if you have a 28" draw,you will most likely cut them so your arrows will be 29" from valley of the nock to back of the point.buy them full lenght and start there.head weight changes your final spine.pick the head weight you want,then glue it to the full length arrow and see how it behaves.then cut and try again until you get good arrow flight.don't do all your arrows at the same time.find what works,then do the rest.hope this helps,steve